Transcription

1 Forensic Spectral Anaylysis: Warm up! The study of triangles has been done since ancient times. Many of the early discoveries about triangles are still used today. We will only be concerned with the "right triangle" (see below) which is a triangle with one of the three angles being 90 degrees. We can use these triangles to determine the heights of buildings, survey property boundaries and determine the length of the waves in the spectrum of colors. Even the heights of mountains on the moon can be determined. This exercise will apply the Pythagorean theorem to calculating wavelengths of light that you will measure. You also will need to do a percent calculation to estimate the error in your result as illustrated below. This illustration above is the general right triangle whose sides have lengths called A, B and C. The angle A is the value in degrees of the angle illustrated. Pythagorean theorem: The ancient Greek mathematical schools discovered that the hypotenuse (side "C" above) of the triangle as well as the sides of the triangle ("A" and "B") are all wonderfully connected in a simple formula. The hypotenuse squared is equal to the sum of the square of each side. This is known as the Pythagorean theorem and can be represented by the following formula: C = A + B ILLUSTRATIVE EXAMPLE: Given: A = 3 and B = 4 if we now want the value of C=? C = = = 25 or 2 C = 25 To find the value of "C" we take the square root of the number since C "squared" means what number times itself will give 25 in this case. The answer in this case is 5. That is, 5 x 5 = 25 or squareroot 25=(25) 1/2 =5 or we would state that C = (25) 1/2 = 5 is the answer for the hypotenuse of a triangle whose sides are 3 and 4. or 5 x 5 =25! ILLUSTRATIVE EXAMPLE: USING THE WINDOWS CALCULATOR set in View as Scientific FOR THIS EXAMPLE WE COULD PROCEED AS FOLLOWS (you can use your own calculator) Enter the 3 and click X^2 key then store in memory with the MS key Enter the 4 and click X^2 key then add to memory with the M+ key Recall the Memory with the MR key (you should have the number 25) Then take the square root by clicking the INV (inverse operation) and the X^2 key. If all goes well you will get a 5 for the answer 2 other portable calculators have M+ and MR and X keys but the square root function has it s own key QUESTION 12. USE A SCIENTIFIC CALCULATOR FOR THE FOLLOWING Given a triangle whose sides are A = 8 and B = 13 find C? C =? The Wavelength( in very small units called Nanometers or nm) of one of the colors produced by a Helium emission spectrum using a device that sets up a right triangle of physical variables is given ultimately as Wavelength = x B/C in nm! 2 2 ILLUSTRATIVE EXAMPLE:Wavelength = x B/C nm with C = ( A + B ) 1/2 by the Pythagorean theorem 2 2 : given A=20 B=10 then C= ( ) 1/2 = ( ) 1/2 = (500) 1/2 =22.36 Hence Wavelength = x B/C= x 10 /22.36 = x = nm units of wavelength. QUESTION14.: Given A =20 B=12 Solve for THE Wavelength using the formula above: Wavelength =?

2 Problem How can we measure the wavelengths of radiation emitted by elements and use them to identify the element? We will explore the colors produced by elements being excited by high voltages (DANGER :DO NOT HANDLE OR TOUCH THE SPECTRUM TUBE APPARATUS while you are touching any plumbing or metal grounds BECAUSE OF THE SHOCK HAZARD. The INSTRUCTOR will demonstrate the correct SAFE handling of the equipment. The dispersion of the colors is produced by a special transparent film called a diffraction grating which looks like a 35 mm glass slide but behaves like a prism or the raindrops that create the rainbow.. See the picture below. Apparatus: Construct the meter stick spectroscope as pictured below: Use the instructors model and this image as a guide. The spectroscope consists of the modified meter stick optical bench: includes meter stick, supports, a diffraction grating, holder with grating(screen holder), a graduated cross stick and holder. Note: Cross stick has an opening slit in the center! Needed Information and Skills It was discovered last century that every element and many compounds will, upon being excited to glow by flame or electricity partial vacuum, produce a unique pattern of colors. Thus, we have a "fingerprint" of an element which can be used to find out whether or not an element is present. How much of the element is present is indicated by the brightness of the unique colors. The brighter the color the greater the amount of the element present. This technique helps scientists determine the composition of many objects. The principles behind the technique you use here is used in medicine to learn about the composition of your blood and, hence,the state of your health. It is also used in criminology to examine various aspects of evidence in crimes and, hence, help solve the crime. The Astronomer analyzes the colors of stars and is able to determine the chemical composition of the Stars as well as motions, temperature etc. and ultimately determine the evolution and fate of stars like our sun. We will be using spectra of colors from excited gases that are called the Emission Spectra. The laboratory contains a SPECTRUM CHART that shows emission spectra from various gases and other types of spectra you encountered in the preparation assignment. The theory on how the grating spreads out light into a spectra depends on the fact that each grating has in our case 600 lines /mm engraved into them. Each of these lines acts as a source of the original light source resulting in 600 images being projected together. This results in waves constructively and destructively interfering with each other. The result is the separation of the colors making up the original source both to the left and right of the original source. You might think of the grating as a device like the prism that separates (disperses) the colors of light produced by glowing objects. We note that the colors within light are waves and are assigned wavelengths (distance between crests of wave). These

3 lengths are very small and are measured as one BILLIONTH of a METER or 10-9 METERS. We give this small unit a name called a NANOMETER ABREVIATED nm. hence, 1 nm = 10-9 meter. Refering to your charts various red colors are around NANOMETERS and Violets are around 400 nm in the size of their wavelengths. NOTE: The laboratory charts are in a meter unit known as an angstrom. Hence, 1nm = 0.1 angstrom or in other words the laboratory charts express visible light as 4000 to 7000 angstrom which in nanometers is 400 to 700. Hence, Just divide any 4 digit angstrom unit by 10 to get a three digit number. USING THE METER STICK SPECTROSCOPE: One look through the grating and through the hole in the cross-stick and centers the gas tube in the opening. The instructor will demonstrate the technique that is illustrated in the following schematic figure. Study this figure keeping in mind the following points: We note in this schematic your eye (see figure) lines up the Spectrum tube image with the OPENING IN THE center of cross stick. Hence, you will use the open slit for aiming. The spectrum of colors are spread out along the cross-stick on the left and right side of the emission tube you aim at. Further note that this exercise is set to work for a distance of 1 meter from the tube to the meter stick as shown in the figure. The colors are the same on either side of the tube image except that the colors closer to the tube are the violet end of the spectrum and the ones further away are the red end. WE WORK WITH THE SPECTRUM TO THE RIGHT (see figure) OF THE TUBE RUNNING FROM VIOLET TO RED IN THIS EXERCISE. In summary: the diffraction grating will split the source of light into two parts. When you look through the grating on the optical bench will see image of the original light source with sets of color images of the source on either side. It is important to center on the meter stick the image of the original spectrum tube when making measurements. The amount of separation seen along the cross-stick called B distance in the figure above of the individual color from the main slit image can by theory beyond this course give us a value for the wavelength. The accurate measuring of the wavelength values determines what element is present in our sample under observation. CALCULATION of WAVELENGTH: The formula for wavelength in NANOMETER units for our diffraction grating apparatus is given from the optical theory of interference in Physics as Wavelength = x B/C In units of nm with C = A 2 + B 2 by the Pythagorean theorem as you can see from the figure We always keep A = 20 centimeters and measure B with our observations. Then we can use this formula to get the wavelength which we do later for the case of helium below.

4 PROCEDURE TO MEASURE THE WAVELENGTHS OF HELIUM 10.Check the setup of the meter stick spectroscope. It is important to set the distance between the cross stick and the grating to 20.0 cm. Thus. the distance A in the figure is fixed at 20 cm or A=20.0 for what follows. BE CAREFUL NOT TO HURT YOUR NEIGHBOR WITH THE METER STICKS BY ACCIDENTALLY POKING THEM. I: B VALUES OF THE TABLE BELOW Reviewing the spectroscope: The grating is in the screen holder. The cross- stick is at right angles to the meter stick optical bench. A = 20 centimeters. USE THE CENTER SLIT OPENING ON THE CROSS-STICK TO AIM THE METER STICK DIRECTLY AT THE CENTRAL IMAGE OF THE TUBE.. The tube source should be about one meter from the cross-stick side of the optical bench. Center the image of the tube and look for first emission line to the right..make SURE OTHER LIGHT SOURCES ARE NOT IN YOUR LINE OF SIGHT OTHERWISE YOU WILL GET LINES FROM THEM!!!!! It helps if you have a partner jot down the values of B for all colors. Which you can place in the table below. NOTE: Take the B MEASUREMENTS FOR THE FOLLOWING COLORS VIOLET, BLUE, STRONG GREEN, YELLOW, STRONG RED, WEAK RED. IGNORE THE WEAK GREEN LINE FOR IT IS NOT ON YOUR CHARTS. For example. If you match A COLOR to the 9 cm. line the distance B is 9 cm. Record this B value in the data table below. You might also note all the other B values for each color at this point. These will range from 7 to 15 cm. II: C VALUES Compute the value of C(see figure) by the Pythagorean theorem C = A 2 + B 2 data table under C column. and record the value(s) in the III: COMPUTE THE WAVELENGTH OF EACH COLOR: the Wavelength IN NANOMETERS by Wavelength = x B/C Record your computed value in the WAVELENGTH column of the data table. This is your computed value. IV; GET THE KNOWN WAVELENGTH VALUES FROM THE CHART: To see how good it is we do the next two steps and get a percent error from the chart(true) value. Consult the large spectrum chart and carefully estimate the value of the wavelength for the yellow line and other colors of Helium and record the values in the CHART:WL column. Thus, CHART:WL is the variable containing the value you read off the chart! V COMPUTE THE % ERROR OF THE WAVELENGTHS: by the following formula WAVELENGTH - CHART:WL % ERROR = X 100 note: negative means Chart:WL> Wavelength CHART:WL HELIUM DATA TABLE A=20 CM computed chart 1' 2' 3' 4' 5' 6' 7' COLOR B C = A 2 + B 2 B / C Wavelength = x B/C WAVELENGTH from CHART % ERROR =(5' -6')/6' X 100 YUCH (EX) = % ("-" means your value < chart) NOTE THE 6 COLORS ARE: VIOLET, BLUE(DIM), GREEN, YELLOW, RED, RED(DIM)

5 Forensic Spectral Analysis: Draw the main lines of the spectrum of the unknowns below. USE THE CHART AND LINK BELOW TO IDENTIFY THE ELEMENT (Link also in class outline) Calculate two primary lines and use the charts to identify the unknown elements or molecules NOTE SPECTRUM WITH THE VIOLET SIDE TO THE LEFT AND RED SIDE TO THE RIGHT! Mark colors and colored lines in appropriate color areas in the rectangular boxes below. Unknown 1 Wavelengths of 2 primary lines = ID= Unknown 2 Wavelengths 2 primary lines = ID= Unknown 3 Wavelength of 2 primary lines= ID= ) Unknown 4 Wavelengths of 2 primary lines= ID= Unknown 5 Wavelengths of 2 primary lines = ID= Unknown 6 Wavelengths of 2 primary lines= ID= LINK to ATOMIC SPECTRA ON THE WEB. Click on a spectra for it's details!

6 Afterthought questions Do these questions after you do the lab. Use the index in "Kutner" and Google if needed to find answers Question 1: Considering Light as a wave the distance between one crest of the wave to the next is called the? Question 2: Approcimately what color would you be observing if you measured a wavelength of light at 600 nm (nano-meters). Question 3: If you measured a wavelength of 10 m (METERS) then you would be observing what type of radiation? Question 4: as in question 3 a wavelength of METERS would be what type of radiation? Question 5: Name two other type of radiations besides light and the types in questions 3 and 4 that are part of the spectrum (electromagnetic radiation)? Question 6 : The band of color from atoms emitting photons of all colors is called a? Question 7: True or False? Each element can emit only certain wavelengths Question 8. What part of the atom falls down to a lower energy level or ground state also emitting a photon of a specific wavelength (color).? We say it makes a transition from one orbit to another Question 9: Define an absorption spectrum Question 10: The wavelength of the Hydrogen alpha (RED) emission line is? nm?. Question 11: The wavelength of the Hydrogen line in the emission spectrum that is Blue in color is called Hydrogen Gamma and has a wavelength of? nm.

Introduction to spectroscopy How do we know what the stars or the Sun are made of? The light of celestial objects contains much information hidden in its detailed color structure. In this lab we will separate

Light and Spectra INTRODUCTION Light and color have intrigued humans since antiquity. In this experiment, you will consider several aspects of light including: a. The visible spectrum of colors (red to

From lowest energy to highest energy, which of the following correctly orders the different categories of electromagnetic radiation? From lowest energy to highest energy, which of the following correctly

Why? Electron Energy and Light How does light reveal the behavior of electrons in an atom? From fireworks to stars, the color of light is useful in finding out what s in matter. The emission of light by

The Nature of Light Light and other forms of radiation carry information to us from distance astronomical objects Visible light is a subset of a huge spectrum of electromagnetic radiation Maxwell pioneered

Activity 17 Electromagnetic Radiation Why? Electromagnetic radiation, which also is called light, is an amazing phenomenon. It carries energy and has characteristics of both particles and waves. We can

Chapter 5 Light and Matter: Reading Messages from the Cosmos Messages Interactions of Light and Matter The interactions determine everything we see, including what we observe in the Universe. What is light?

Fall 2003 Emission Spectra of Elements Purpose: To compare and contrast the emission spectra of various gases. Investigate quantitatively the emission spectrum of hydrogen and relate it to Bohr's theory

5. The Nature of Light Light travels in vacuum at 3.0. 10 8 m/s Light is one form of electromagnetic radiation Continuous radiation: Based on temperature Wien s Law & the Stefan-Boltzmann Law Light has

Experiment #5: Qualitative Absorption Spectroscopy One of the most important areas in the field of analytical chemistry is that of spectroscopy. In general terms, spectroscopy deals with the interactions

Practice Test IV Name 1) In a single slit diffraction experiment, the width of the slit is 3.1 10-5 m and the distance from the slit to the screen is 2.2 m. If the beam of light of wavelength 600 nm passes

The Electromagnetic Spectrum 1 Look around you. What do you see? You might say "people, desks, and papers." What you really see is light bouncing off people, desks, and papers. You can only see objects

Old Science 30 Physics Practice Test A on Fields and EMR Test Solutions on the Portal Site Use the following image to answer the next question 1. Which of the following rows identifies the electrical charge

II The Nature of Electromagnetic Radiation The Sun s energy has traveled across space as electromagnetic radiation, and that is the form in which it arrives on Earth. It is this radiation that determines

Lesson Summary Students use the spectrograph from the Building a Fancy Spectrograph lesson to gather data about light sources. Using the data they ve collected, students are able to make comparisons between

WAVES AND ELECTROMAGNETIC RADIATION All waves are characterized by their wavelength, frequency and speed. Wavelength (lambda, ): the distance between any 2 successive crests or troughs. Frequency (nu,):

Spectrophotometry and the Beer-Lambert Law: An Important Analytical Technique in Chemistry Jon H. Hardesty, PhD and Bassam Attili, PhD Collin College Department of Chemistry Introduction: In the last lab

INTRODUCTION Most students have encountered rainbows, either spotting them directly on those special days when the raindrops fall while the Sun still finds cloudless regions to peek through, or at least

VISIBLE SPECTROSCOPY Visible spectroscopy is the study of the interaction of radiation from the visible part (λ = 380-720 nm) of the electromagnetic spectrum with a chemical species. Quantifying the interaction

grades K 5 Objective This activity offers two simple ways to demonstrate that white light is made of different colors of light mixed together. The first uses special glasses to reveal the colors that make

The Photoelectric Effect. The Wave particle duality of light Light, like any other E.M.R (electromagnetic radiation) has got a dual nature. That is there are experiments that prove that it is made up of

Light PSC 203 Overview In this section: What is light? What is the EM Spectrum? How is light created? What can we learn from light? In-class activity Discuss your answers in groups of 2 Think of as many

Newton s laws of motion and gravity 1. Every body continues in a state of rest or uniform motion (constant velocity) in a straight line unless acted on by a force. (A deeper statement of this law is that

PRACTICE EXAM IV P202 SPRING 2004 1. In two separate double slit experiments, an interference pattern is observed on a screen. In the first experiment, violet light (λ = 754 nm) is used and a second-order

BACKGROUND INFORMATION Infrared Spectroscopy Before introducing the subject of IR spectroscopy, we must first review some aspects of the electromagnetic spectrum. The electromagnetic spectrum is composed

How is LASER light different from white light? Teacher Notes Concepts: (1) Light is a type of energy that travels as waves. [6.2.3.1.1] (2) Laser light is different from traditional light sources and must

Atoms Absorb & Emit Light Spectra The wavelength of the light that an element emits or absorbs is its fingerprint. Atoms emit and absorb light First Test is Thurs, Feb 1 st About 30 multiple choice questions

grades 6 1 2 Objective Build a simple, pocket-sized spectroscope from readily available materials and use it to examine different kinds of light sources in school, at home, and around the city. Introduction

Waves Sound and Light r2 c:\files\courses\1710\spr12\wavetrans.doc Ron Robertson The Nature of Waves Waves are a type of energy transmission that results from a periodic disturbance (vibration). They are

INSURANCE SCAM OPTICS - LABORATORY INVESTIGATION P R E A M B L E The original form of the problem is an Experimental Group Research Project, undertaken by students organised into small groups working as

INTRODUCTION Fibre optics behave quite different to metal cables. The concept of information transmission is the same though. We need to take a "carrier" signal, identify a signal parameter we can modulate,

Exercises 28.1 The Spectrum (pages 555 556) 1. Isaac Newton was the first person to do a systematic study of color. 2. Circle the letter of each statement that is true about Newton s study of color. a.

Astronomy 114 Summary of Important Concepts #1 1 1 Kepler s Third Law Kepler discovered that the size of a planet s orbit (the semi-major axis of the ellipse) is simply related to sidereal period of the

Light and radiation Light is a type of electromagnetic (EM) radiation, and light has energy. Many kinds of light exist. Ultraviolet (UV) light causes skin to tan or burn. Infrared (IR) light is used in

Interference Physics 102 Workshop #3 Name: Lab Partner(s): Instructor: Time of Workshop: General Instructions Workshop exercises are to be carried out in groups of three. One report per group is due by

UV/Vis Spectroscopy Varka Evi-Maria Ph.D. Chemist AUTH Thessaloniki 2012 Introduction of Spectroscopy The structure of new synthesised molecules or isolated compounds from natural sources in the lab must

Physics 30 Worksheet # 14: Michelson Experiment 1. The speed of light found by a Michelson experiment was found to be 2.90 x 10 8 m/s. If the two hills were 20.0 km apart, what was the frequency of the

Preview of Period 3: Electromagnetic Waves Radiant Energy II 3.1 Radiant Energy from the Sun How is light reflected and transmitted? What is polarized light? 3.2 Energy Transfer with Radiant Energy How

What s in the Mix? Liquid Color Spectroscopy Lab (Randy Landsberg & Bill Fisher) Introduction: There is more to a color than a name. Color can tell us lots of information. In this lab you will use a spectrophotometer

THE BOHR QUANTUM MODEL INTRODUCTION When light from a low-pressure gas is subject to an electric discharge, a discrete line spectrum is emitted. When light from such a low-pressure gas is examined with

H9 Modeling the Expanding Universe Activity H9 Grade Level: 8 12 Source: This activity is produced by the Universe Forum at NASA s Office of Space Science, along with their Structure and Evolution of the

Using the Spectrophotometer Introduction In this exercise, you will learn the basic principals of spectrophotometry and and serial dilution and their practical application. You will need these skills to

Lecture 7: Light Waves Isaac Newton (1643-1727) was born in the year Galileo died He discovered the Law of Gravitation in 1665 He developed the Laws of Mechanics that govern all motions In order to solve

Principles of Imaging Science I (RAD119) Electromagnetic Radiation Energy Definition of energy Ability to do work Physicist s definition of work Work = force x distance Force acting upon object over distance

LIGHT AND ELECTROMAGNETIC RADIATION Light is a Wave Light is a wave motion of radiation energy in space. We can characterize a wave by three numbers: - wavelength - frequency - speed Shown here is precisely

PURPOSE In this experiment we will use the diffraction grating and the spectrometer to measure wavelengths in the mercury spectrum. THEORY A diffraction grating is essentially a series of parallel equidistant

Q. The diagram below shows the range of wavelengths and frequencies for all the types of radiation in the electromagnetic spectrum. X-rays, which have frequencies in the range 0 8 0 2 Hz are already marked

Name The Relationship Between Wavelength and Frequency in the Electromagnetic Spectrum Purpose: To discover and verify the relationship between Wavelength and Frequency of the Electromagnetic Spectrum.

Atomic Structure Ron Robertson r2 n:\files\courses\1110-20\2010 possible slides for web\atomicstructuretrans.doc I. What is Light? Debate in 1600's: Since waves or particles can transfer energy, what is

Q. The diagram below shows the range of wavelengths and frequencies for all the types of radiation in the electromagnetic spectrum. X rays, which have frequencies in the range 0 8 0 2 Hz are already marked

Atomic Structure: Chapter Problems Bohr Model Class Work 1. Describe the nuclear model of the atom. 2. Explain the problems with the nuclear model of the atom. 3. According to Niels Bohr, what does n stand

Emission of Light & Atomic Models 1 Objective At the end of this activity you should be able to: o Explain what photons are, and be able to calculate their energies given either their frequency or wavelength.

Semester 2 Final Exam Review Motion and Force Vocab Motion object changes position relative to a reference point. Speed distance traveled in a period of time. Velocity speed in a direction. Acceleration

Diffraction of Laser Light No Prelab Introduction The laser is a unique light source because its light is coherent and monochromatic. Coherent light is made up of waves, which are all in phase. Monochromatic

Spectrophotometry Reading assignment:. http://en.wikipedia.org/wiki/beer-lambert_law Goals We will study the spectral properties of a transition metal-containing compound. We will also study the relationship

Adapted from State of Delaware TOE Unit MAKING SENSE OF ENERGY Electromagnetic Waves GOALS: In this Part of the unit you will Learn about electromagnetic waves, how they are grouped, and how each group

Eighth Grade Electromagnetic Radiation and Light Assessment 1a. Light waves are the only waves that can travel through. a. space b. solids 1b. Electromagnetic waves, such as light, are the only kind of

Section 1 Electromagnetic Waves What are electromagnetic waves? What do microwaves, cell phones, police radar, television, and X-rays have in common? All of them use electromagnetic waves Electromagnetic